Lamps typically are replaced either according to a pre-determined schedule or after they burn out. The pre-determined schedule is usually a rough estimate of when lamps will be near their end of life based on the lamp's published lamp life (defined in hours of operation) and the lamp's expected usage. Neither replacement method is particularly desirable. Replacing lamps according to a schedule may unnecessarily increase lamp replacement costs and environmental waste if the replaced lamps still have many hours of lamp life remaining. Replacing lamps after they burn out causes at least some inconvenience and may result in hazardous or dangerous conditions until the lamps are replaced. Unfortunately, nothing is currently known that can automatically alert a user to a lamp's pending end of life based on actual usage of the lamp.
Occupancy sensors automatically control the operation of lights and are used to save energy and lamp life by turning off lights in areas that are unoccupied. When the presence of one or more persons is detected by the occupancy sensor, the sensor turns on or keeps on the lights controlled by the sensor. However, the lamp life of a fluorescent lamp decreases as the number of starts (i.e., off/on transitions) increases. That is, each off/on transition reduces the lamp's operating hours by a small amount. Thus, if lights are turned off and then back on again after too short a period of off time, more lamp life is lost by the affect of the lights turning back on than is saved by the short off time.
To help prevent lights from unnecessarily turning off and on too frequently, occupancy sensors typically have a short time delay that keeps lights on after occupancy is last detected. Should an occupant return within the time delay, the lights will remain on, thus avoiding an off/on transition. However, this feature may not extend lamp life if the actual occupancy pattern does not conform to the time delay. For example, if occupants tend to leave and return just after expiration of the sensor's time delay, no off/on transitions are avoided and loss of lamp life is accelerated.
This time delay is programmable in some known occupancy sensors. However, nothing is currently known that can automatically select the optimal time delay based on actual occupancy patterns. Thus, a user is likely to select a time delay based on a predicted occupancy pattern, which may or may not result in any lamp life savings.
In view of the foregoing, it would be desirable to be able to provide an occupancy sensor that can be programmed to monitor and report lamp life status to a user.
It would also be desirable to be able to provide an occupancy sensor that can automatically select the optimal time delay based on an actual occupancy pattern detected by the sensor.